Air Photonics
Résumé
Modern ultrashort laser sources routinely produce powerful enough pulses to ionize the ambient air, so that the very atmosphere we breath becomes an interesting medium for nonlinear photonics. One of the first and most prominent ultrafast nonlinear effects studied in air is filamentation [1,2], and so-called femtosecond filaments have enabled many applications, for example remote supercontinuum generation [3] or pulse compression [4,5], for review see [6,7]. Air lasing [8] offering exciting possibilities for standoff detection [9] has been demonstrated. Moreover, air is easily exploited as nonlinear medium in hollow-core photonic crystal fibers [10]. One of the most intriguing air photonics application is certainly the generation of broadband THz radiation in an air plasma produced by a two-color laser pulse composed of fundamental and its second harmonic frequency. First attributed to a four-wave mixing process [11], it is nowadays well established that photo currents in the laser generated plasma are responsible for the THz emission [12]. Spectral properties of the radiation produced can be understood by the local current (LC) model [13], and the elongated shape of the plasma favours forwards THz emission [14]. Several methods have been proposed to increase the THz energy yield of such laser-plasma based sources: Optimizing the pump waveform by employing, e.g., three pump colors [15], exploiting the scaling of the THz emission with the fundamental pump wavelength [16,17], or going beyond using linearly polarized pump pulses [18,19]. Another intriguing aspect of THz wave air photonics is that with air biased coherend detection (ABCD) [20] a broadband and robust THz detection scheme is available that is readily combined with the previously discussed source [21,22] to obtain a versatile THz platform.
Origine : Fichiers produits par l'(les) auteur(s)